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Q.
Sodium chloride has rock salt structure, how many molecules are there in the unit cell of $NaCl$
NTA AbhyasNTA Abhyas 2022
Solution:
In $NaCl$ (rock salt): Number of $Na^{+}$ ions $=12$ (at edge centers) $\frac{1}{4}+1$ (at body centre) × 1 =4.
Number of $Cl^{-}$ ions $=8$ (at corners) $\times \frac{1}{8}+6$ (at face centre) $\times \frac{1}{2}=4$ .
Thus $4$ formula units per unit cell.